The doming of a shadow mask in color cathode ray tube is caused by thermal expansion of the mask due to the heat generated by the impinging electron beams. Since the mask comprises a fragile foraminated member attached at its peripheral edge to a relatively heavy frame, the fragile portion expands more rapidly than the frame, causing the fragile portion to expand outwardly toward the phosphor screen, a condition called "doming". This doming effects the critical alignment between the apertures in the mask and the discrete phosphor areas of the screen with which they are aligned, causing mis-registration of the beams and color dilution.
The art has long been aware of this condition, and many solutions have been proposed. Among the most successful have been bi-metallic mounting means for the mask-frame assembly such as those shown in U.S. Pat. Nos. 3,524,973; 3,524,974; and 3,803,436.